1. Field of the Invention
The present invention relates to a batch mixer for mixing polymer resin materials such as plastic and rubber, and a mixing rotor used in the batch mixer
2. Description of the Prior Art
A batch mixer is designed to produce a mixed product for one batch with a series of actions where after mixing materials such as rubber and plastic are pressed into a chamber by a floating weight, the materials are mixed by a pair of mixing rotors provided in the chamber, and the mixing materials are discharged from the chamber to the outside via a drop door when the mixing materials reached a desired mixing state.
As this type of mixer, there are known a batch mixer (refer to U.S. Pat. No. 5,984,516 publication) which is capable of mixing various types of mixing materials without replacing mixing rotors and, at the same time, securing the quality of the mixing materials to be obtained without sacrificing inherent processing performance of the apparatus, a mixer (refer to European Patent No. 1033217 publication) where mixing and dispersion of the mixing materials processed by one mixing wing are effectively balanced and the mixing is properly controlled where both the mixing and the dispersion are compatible, and the like.
The mixing rotors shown in the U.S. Pat. No. 5,984,516 publication are used in a batch mixer, where two or more wing sections consisting of a long wing and a short wing are formed on each mixing rotor in the circumference direction, gaps (tip clearance) between wing top portions of the wing sections in the axis direction and the circumference direction and a chamber inner wall surface are changed in two or more of large, medium and small.
Reasons for varying the tip clearance of the wing sections of the mixing rotors are as follows. Specifically, the wing having a narrow tip clearance allows a major part of the mixing materials on the forward movement side of the tip clearance to move in the axis direction, impart strong shearing force to the mixing materials to promote the dispersion, and can improve a mastication effect of natural rubber. Further, by scraping off the surface layer of the mixing materials attached on the chamber inner wall surface, cooling efficiency by the chamber inner wall surface having a cooling structure can be increased, and excessive increase of temperature caused by strong shearing force can be suppressed.
On one hand, wings having a large tip clearance promote the movement of the mixing materials in the circumference direction by allowing a major part of the mixing materials on the forward movement side of the tip clearance to pass the clearance, mix the materials to apply an even shearing action to the mixing materials, and excessive increase of temperature of the mixed product can be suppressed even when the number of wings of the mixing rotors increases because the shearing force applied to the mixing materials by the wings is controlled at a low level.
On the other hand, the mixing rotors shown in the European Patent No.1033217 publication are used in a batch mixer and a continuous mixer. In the mixing rotors, the twist angle of the mixing wings, which are developed into a plane state around their axis center, varies from its origin to end-point to make a developed shape of the mixing wings from the origin to the end-point substantially become a non-linear shape. Thus, the flow of the mixing materials in the axis direction and the circumference direction is controlled, and a mixing effect and a dispersion effect can be compatible in a well-balanced manner.
In other words, a material flow of the mixing materials in the axis direction is generated to improve the mixing effect of the mixing materials by the origin portion of the mixing wing, which has a large twist angle, while the amount of the mixing materials passing though the tip clearance is secured at the end-point portion having a small twist angle, and thus the dispersion effect of the mixing materials can be improved.
However, in the constitution of the above-described prior art, when the number of wings is increased to three or more in order to increase the biting speed of the mixing materials into the chamber to improve the production efficiency, the temperature of the mixing materials increases and the mixing quality of a mixed product reduces due to the increase of heating value caused by shearing, the effective volume of the chamber reduces to decrease the production efficiency due to the increase of the volume proportion of the rotors within the chamber, and a shorter distance between adjacent mixing wings and an increased rotor surface area allow the mixing materials to attach to the surface of the mixing wings to reduce the mixing quality and the production efficiency.
Generally, the temperature increase of the mixing materials is suppressed by reducing the charge amount of the mixing materials into the chamber or reducing the rotation number of rotors, and similarly, the attaching of the mixing materials to the surface of the mixing wings is controlled by reducing the charge amount of the mixing materials into the chamber.
However, to make the improvement of the production efficiency compatible with maintaining/improving the mixing quality, sacrificing the inherent processing performance of the mixer, that is, reducing the rotation number of the mixing rotors or reducing the charge amount of the mixing materials is an unpractical countermeasure.